#ifdef _WIN32
#define getc_unlocked(stdin) getc(stdin)
#endif
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <string>
#include <list>
#include <bitset>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <cmath>
#include <cassert>
#include <ctime>
#include <numeric>
#include <functional>
#include <valarray>
#include <complex>
using namespace std;

const int dx[]={0,-1,0,1,-1,1, 1,-1};
const int dy[]={1,0,-1,0, 1,1,-1,-1};
const double eps=1e-8;

typedef long long LL;
typedef unsigned long long uLL;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vgraph;
typedef vector<pii> vpii;
typedef vector<LL> vLL;
typedef vector<string> vs;

#define sz(a) a.size()
#define fori(i,a,b) for(int i(a),_b(b);i<=_b;++i)
#define ford(i,a,b) for(int i(a),_b(b);i>=_b;--i)
#define forn(i,n) fori(i,0,n-1)
#define fora(i,a) forn(i,sz(a))
#define fore(it,c) for(typeof((c).begin()) it=(c).begin();it!=(c).end();++it)
#define all(a) a.begin(),a.end()
#define mp make_pair
#define pb push_back
#define clear0(a) memset(a,0,sizeof(a))
#define clearm1(a) memset(a,-1,sizeof(a))
#define maximum(a) (*max_element(all(a)))
#define minimum(a) (*min_element(all(a)))
#define findx(a,x) (find(all(a),x)-a.begin())
#define two(X) (1LL<<(X))
#define contain(S,X) ((S)&two(X))
#define setbit(S,X) ((S)|=two(X))
#define clearbit(S,X) ((S)&=~two(X))
#define togglebit(S,X) ((S)^=two(X))
#define sqr(a) ((a)*(a))
#define fi "input.inp"
#define fo "output.out"
#define nmax 100
#define mmax 100
#define kmax 10
#define modulo 1000000007
#define maxc 999999999

class FoxProgression {
public:
	int theCount(vector <int> seq) {
		int n=sz(seq);
		if (n<=1) return -1;
		double qm=1.0*seq[1]/seq[0];
		int qp=seq[1]-seq[0],kq1=1;
		int kq2=abs(qm-int(qm))<=eps;
		fori(i,2,n-1)
		{
			 if (abs(qm-1.0*seq[i]/seq[i-1])>eps) kq2=0;
			 if (qp!=seq[i]-seq[i-1]) kq1=0;
		}
		if (kq1==kq2 && kq1==1)
			if (abs(seq[n-1]*qm-seq[n-1]+qp)<=eps) kq1=0;
		return kq1+kq2;
	}
};


// BEGIN KAWIGIEDIT TESTING
// Generated by KawigiEdit-pf 2.3.0
#include <iostream>
#include <string>
#include <vector>
#include <ctime>
#include <cmath>
using namespace std;
bool KawigiEdit_RunTest(int testNum, vector <int> p0, bool hasAnswer, int p1) {
	cout << "Test " << testNum << ": [" << "{";
	for (int i = 0; int(p0.size()) > i; ++i) {
		if (i > 0) {
			cout << ",";
		}
		cout << p0[i];
	}
	cout << "}";
	cout << "]" << endl;
	FoxProgression *obj;
	int answer;
	obj = new FoxProgression();
	clock_t startTime = clock();
	answer = obj->theCount(p0);
	clock_t endTime = clock();
	delete obj;
	bool res;
	res = true;
	cout << "Time: " << double(endTime - startTime) / CLOCKS_PER_SEC << " seconds" << endl;
	if (hasAnswer) {
		cout << "Desired answer:" << endl;
		cout << "\t" << p1 << endl;
	}
	cout << "Your answer:" << endl;
	cout << "\t" << answer << endl;
	if (hasAnswer) {
		res = answer == p1;
	}
	if (!res) {
		cout << "DOESN'T MATCH!!!!" << endl;
	} else if (double(endTime - startTime) / CLOCKS_PER_SEC >= 2) {
		cout << "FAIL the timeout" << endl;
		res = false;
	} else if (hasAnswer) {
		cout << "Match :-)" << endl;
	} else {
		cout << "OK, but is it right?" << endl;
	}
	cout << "" << endl;
	return res;
}
int main() {
	bool all_right;
	bool disabled;
	bool tests_disabled;
	all_right = true;
	tests_disabled = false;
	
	vector <int> p0;
	int p1;
	
	{
	// ----- test 0 -----
	disabled = false;
	int t0[] = {1,2,4,8};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = 1;
	all_right = (disabled || KawigiEdit_RunTest(0, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	{
	// ----- test 1 -----
	disabled = false;
	int t0[] = {5,3,1};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = 1;
	all_right = (disabled || KawigiEdit_RunTest(1, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	{
	// ----- test 2 -----
	disabled = false;
	int t0[] = {1,1};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = 1;
	all_right = (disabled || KawigiEdit_RunTest(2, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	{
	// ----- test 3 -----
	disabled = false;
	int t0[] = {8,4};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = 1;
	all_right = (disabled || KawigiEdit_RunTest(3, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	{
	// ----- test 4 -----
	disabled = false;
	int t0[] = {1};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = -1;
	all_right = (disabled || KawigiEdit_RunTest(4, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	{
	// ----- test 5 -----
	disabled = false;
	int t0[] = {4,8};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = 2;
	all_right = (disabled || KawigiEdit_RunTest(5, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	{
	// ----- test 6 -----
	disabled = false;
	int t0[] = {1,3,4};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = 0;
	all_right = (disabled || KawigiEdit_RunTest(6, p0, true, p1) ) && all_right;
	tests_disabled = tests_disabled || disabled;
	// ------------------
	}
	
	if (all_right) {
		if (tests_disabled) {
			cout << "You're a stud (but some test cases were disabled)!" << endl;
		} else {
			cout << "You're a stud (at least on given cases)!" << endl;
		}
	} else {
		cout << "Some of the test cases had errors." << endl;
	}
	return 0;
}
// END KAWIGIEDIT TESTING
//Powered by KawigiEdit-pf 2.3.0!
